Requisite to all magnetic data storage systems are a magnetic data recording media for storing data in magnetic form and an electromagnetic transducer having one or more "heads" for performing "reading" and/or "writing" of data in magnetic form, respectively from or onto the recording media. While such magnetic data storage systems have utilized data recording media of various configuration (such as tapes, rigid disks and drums), the so-called "floppy disk" media has recently found wide applicability not only in program storage and entry applications, but also in a number of diverse data entry, storage and control applications. The "floppy disk" media is a thin, generally planar flexible or pliant magnetic disk having magnetically sensitive surfaces and currently rotatable at speeds of approximately 360 rpm, within a protective envelope or jacket cover. Data transfer to and from the floppy disk is achieved by one or more electromagnetic heads arranged within, and collectively forming a transducer. The transducer (or transducers) communicate with one or both surfaces of the floppy disk through window openings in the protective envelope.
A number of various transducer structures useful for communicating with floppy disks have appeared in the prior art. In general, those portions of such transducers that are responsible for the electromagnetic transfer to and from the floppy disk, have not significantly differed from one another in their basic component pieces. Each such transducer basically comprises a plurality of magnetic core members prepositioned with respect to one another, secured together and interconnected with one or more coils, to define an operable electromagnetic transducer. For the most part, such transducer structures, as used in association with data transfer to and from a floppy disk, have comprised a single channel read/write head, and may typically also include an eraser head. The eraser head generally comprises a plurality of erase cores for trimming a "track" of information written onto the floppy disk surface, and for erasing a pair of guard-band areas on each side of the trimmed track. For the purpose of this invention, the particular structural details and relative placement of the electromagnetic components which collectively comprise the various head portions of an electromagnetic transducer are not important per se, since this invention applies equally well to any electromagnetically operative "type" of such transducer and component head structures thereof, whether they are multiple or single, erase, read, write, or combination read/write heads.
In the initially introduced single-sided systems, electromagnetic data transfer between the transducer and floppy disk is possible only to one side of the floppy disk at a time. Efficiency is significantly improved with a double sided system. In such a system, data transfer to both sides of the floppy disk is possible at the same time. This is made possible through the use of a pair of generally opposed transducers, operatively disposed to sandwich the floppy disk therebetween, thus simultaneously engaging both surfaces of the floppy disk.
Floppy disk systems of the prior art, both single and double sided, have typically mounted their respective transducer "assemblies" upon a movable carriage structure which is radially indexed with respect to a relatively fixed position floppy disk. Movement of the carriage structure enables the transducer or transducers carried thereby to access different desired circular "tracks" located at different radial positions on the magnetizable surface of the floppy disk. Positioning of the movable carriage structure must be aligned and controlled with respect to the nominal disk plane, which is defined as that plane in which a surface of a floppy disk nominally lies during operative rotation of the disk. Since a floppy disk has two data transfer surfaces that are separated by the thickness of the floppy disk, a double sided system will be concerned with two nominal disk planes, generally referred to as "upper" and "lower" nominal disk planes. In an optimally operative system, except for that portion of the floppy disk that is engaged by the transducers, it is desirable for the two data transfer surfaces of the floppy disk to lie perfectly planar respectively in the upper and lower nominal disk planes, with no imperfections therein, such as wobble, or deformation caused for example by imperfections in the disk itself, by the flexible nature of the disk or by motion transmitted to the disk by the apparatus rotating the disk.
Prior art floppy disk data transferring systems have differed in their designs of the transducer support structures that are mounted to the movable carriage. In early single sided floppy disk systems, the transducer generally had a curved surface for operably engaging the floppy disk and for penetrating into and beyond the nominal disk plane of the engaged data transfer surface. The transducer was generally fixedly mounted to the movable carriage. A hinge arm carrying a pressure pad was pivotally mounted to the carriage to allow for disk entry. The arm was spring loaded, such that the pressure pad carried thereby engaged the disk at a location directly opposite the transducer head, and applied a known force to the disk, conforming the pliant disk into intimate engagement with the curved transducer head. This early single sided system offered limited capacity in data transfer since data transfer to only one side of the disk at a time could be achieved, and was thus relatively slow.
Larger capacity and faster data access and transfer requirements have resulted in double sided data transfer floppy disk systems, having the capability of simultaneously transferring data with both sides of a floppy disk. As above stated, such systems generally have a pair of transducers mounted to operatively engage opposite surfaces or sides of the floppy disk, in generally opposed relationship to one another. The opposed transducers are generally positioned such that their respective head "gaps" are slightly radially offset relative to one another, for minimizing magnetic flux interaction between the transducers.
In such prior art double sided floppy disk data transfer systems, the upper and lower recording surface areas of the floppy disk may periodically move out of their respective upper and lower nominal disk planes. Such deviations could, for example, be caused by distorted disks or excessive disk wobble (i.e., perturbations in the disk surfaces as the disk rotates). It has therefore been thought to be desirable for the oppositely disposed transducer heads to be movably mounted in opposition to one another, so that the transducer heads could follow the actual path of the floppy disk recording surfaces passing therebetween, as they deviated from the upper and lower nominal disk planes. Accordingly, various transducer mounting arrangements have been devised in the prior art, to accommodate such deviations in floppy disk operative movement.
One such mounting configuration, described in U.S. Pat. No. Re. 29,380, reissued Aug. 30, 1977, illustrates a method of mounting a pair of transducer slider heads in opposing relationship upon a pair of fixed support arms, movable under solenoid action, toward and into engagement with the disk in a "loading" operation, and away from and out of engagement with the disk during a "unloading" operation. The support arms engage stop members on a carriage to limit the closure distance therebetween to a fixed predetermined amount. The opposing transducer heads are urged into forceable engagement with the disk by a pair of coil springs underlying the transducer heads, to sandwich the floppy disk therebetween.
As pointed out more fully in copending application entitled "Z-Axis Flexure Suspension Apparatus" by Leonard Kronfeld, Ser. No. 82,009, filed Oct. 5, 1979, and assigned to the same assignee as the present application, such a structure is subject to certain disadvantages in terms of lack of sensitivity of movement to follow deviations of the floppy disk, introduction of data transfer errors caused by shifting of the transducers relative to the recording tracks, slow damping response following a loading operation, and reduced intimacy of contact between the transducer heads and the recording surfaces of the floppy disk.
Another variation of a dual transducer mounting configuration is described in U.S. Pat. No. 4,089,029 issued May 9, 1978. In that structure, a pair of transducers mounted on long cantilevered support arms are mechanically urged together under spring bias, with each of the oppositely disposed transducers carried thereby being independently mounted on a gimbal structure which allows universal pivotal motion of the respective transducer head assemblies. The disk engaging surfaces of the transducer heads are generally planar. The pivoted transducer support arms are interlocked such that motion of one such arm tending to raise one of the transducers from engagement with the surface of the disk also moves the second arm so as to move the second transducer from the opposing surface of the disk, for loading and unloading the disk into and out of operative position. Each arm is urged with a predetermined force against its corresponding side of the disk, tending to maintain intimate contact between the transducer carried by that arm and its respectively engaged disk surface. The composite structure sandwiches the floppy disk between the opposed transducers at a relatively weak loading force of six to seven grams, which tends to give rise to instability. Also, while the double-gimballed structure is configured to enable rapid responsive movement of the transducer heads to accomodate perturbations in disk movement out of the Nominal Disk Planes, such transducer tracking movements give rise to shifting or offset errors, as pointed out in greater detail in the above-identified copending application. The system is very complicated and expensive to construct and manufacture.
A relatively recent configuration of a double sided floppy disk data transfer system is disclosed in U.S. Pat. No. 4,151,573 issued Apr. 24, 1979. This structure is configured to improve the intimacy of contact between the transducer disk surfaces and to reduce some of the disadvantages of the prior double-gimbal transducer support structure. This structure uses an asymmetrical transducer support structure having a first or lower transducer with a planar transducer core surface that is immovably fixed (as in early single-sided transfer systems). A second (upper) transducer is mounted on a universally movable gimbal structure and is pivotally movable by a spring loaded arm into operative proximity with the fixed lower transducer head so as to sandwich the floppy disk therebetween at a predetermined force. The lower transducer head structure is sized (in surface area) relatively larger than the upper transducer head, so as to extend considerably beyond the outline dimensions of the upper core transducer. The core surface of the lower transducer is mounted so as to penetrate excessively into the nominal disk plane of a loaded floppy disk, and the upper transducer carried by the gimballed support structure acts as a pressure pad for the lower fixed transducer head. Conversely, the lower fixed transducer head acts as a pressure pad for the upper transducer core. While reducing some of the shifting and offset tracking errors inherent in the double gimbal structures described above, this structure still experiences some mispositioning of the transducer relative to the recording tracks of the lower surface of the floppy disk, due to the fixed nature of the lower transducer head. The structure according to that patent also has the disadvantage of excessive wear on the floppy disk due to the "hard" landing of the upper transducer during loading of the system. These particular shortcomings of the prior art are overcome by the improvement disclosed and claimed in the above-identified copending application.